This application is based on Japanese Patent Applications HEI No. 10-371420 filed on Dec. 25, 1999 and HEI No. 10-373058 filed on Dec. 28, 1999, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device wherein liquid crystal molecules are vertically aligned (homeotropic alignment) between opposing substrates when no electric field is applied and one pixel is divided into a plurality of domains.
b) Description of the Related Art
FIGS. 25A to 25C are schematic cross sectional views of a conventional liquid crystal display device of a homeotropic alignment type, respectively illustrating a black display state, a halftone display state, and a white display state. Liquid crystal material containing liquid crystal molecules having a negative dielectric anisotropy is filled in between a pair of substrates 100 and 101. Polarizer plates are disposed outside of the substrates 100 and 101, with their polarizing axes crossing at a right angle.
As shown in FIG. 25A, when a voltage is not applied, the liquid crystal molecules 102 are aligned vertically relative to the substrates 100 and 101 and produce black color. As a voltage is applied across the substrates to align the liquid crystal molecules 102 in parallel to the substrates as shown in FIG. 25C, the polarization direction of light passing through the liquid crystal layer rotates and white color is produced.
As shown in FIG. 25B, as a voltage is applied which is lower than that when the white image is produced, the liquid crystal molecules 102 are aligned obliquely relative to the substrate. A halftone image is obtained by light L1 propagating along a direction perpendicular to the substrates. Light propagating from the lower right to upper left as viewed in FIG. 25B rarely receives the birefringence effect of the liquid crystal layer. Therefore, when the display screen is viewed from the upper left, it becomes black. Contrary, light propagating from the lower left to upper right as viewed in FIG. 25B considerably receives the birefringence effect of the liquid crystal layer. Therefore, when the display screen is viewed from the upper right, it becomes white. As above, a homeotropic type liquid crystal display device is generally has poor visual angle characteristics in the halftone display state.
The visual angle characteristics of a conventional homeotropic type liquid crystal are poor in the halftone display state, as described above.
It is an object of the present invention to provide a homeotropic type liquid crystal display device having improved visual angle characteristics.
According to one aspect of the present invention, there is provided a liquid crystal display device, comprising: first and second substrates disposed in parallel at a gap therebetween; liquid crystal material containing liquid crystal molecules having negative dielectric anisotropy, said liquid crystal material being filled in the gap between said first and second substrates; alignment film for homeotropically aligning the liquid crystal molecules in a state of no electric field; pixel electrodes formed on an opposing surface of said first substrate and regularly disposed in row and column directions; a common electrode formed on an opposing surface of said second substrate; data bus lines disposed on the opposing surface of said first substrate, each data bus line being provided in correspondence with each column of said pixel electrodes; gate bus lines disposed on the opposing surface of said first substrate, each gate bus line being provided in correspondence with each row of said pixel electrodes, said gate bus line being disposed passing an inside area of said pixel electrode at a corresponding row, as viewed along a substrate normal direction; switching elements disposed on the opposing surface of said first substrate, each switching element being provided in correspondence with each pixel electrode, each switching element connecting a corresponding pixel electrode and a corresponding data bus line and being switched between a conduction state and a non-conduction state in response to an externally applied control signal; gate connection lines, each gate connection line being provided for each switching element, each gate connection line transferring the control signal from the gate bus line, corresponding to a row different from a row of the pixel electrode connected to corresponding switching element, to corresponding switching element; protrusions formed on the opposing surface of one of said first and second substrates, said protrusions dividing an area of said pixel electrode into a plurality of areas and each protrusion being bent at a point where the protrusion intersects with the gate bus line as viewed along the substrate normal direction; and domain border regulating structure formed on the opposing surface of the other of said first and second substrates, said domain border regulating structure being disposed at a distance from each of said protrusions as viewed along the substrate normal direction, said domain border regulating structure defining, together with said protrusions, borders of each domain in which a tilt direction of the liquid crystal molecules is uniform when a voltage is applied across said pixel electrode and said common electrode.
The protrusion and domain border regulating structure divide an area of each pixel into a plurality of domains. In each domain, the tilt direction of liquid crystal molecules is uniform when a voltage is applied. Since a plurality of domains having various tilt directions are formed, the visual angle characteristics can be improved. The gate bus line prevents leak light to be caused by disturbed alignment of liquid crystal molecules near the flection point of the protrusion. Further, since auxiliary capacitance is formed between the gate bus line and pixel electrode, a voltage fluctuation of the pixel electrode to be caused by a voltage change of the data bus line can be suppressed.